1. Field of the Invention
The present invention relates to a device for radiating an ultrasound into a material by means of using an assembly composed of a piezoelectric substrate, a first input-, a second input-, and an output interdigital transducers.
2. Description of the Prior Art
In constructing an acoustical system, a transducer for emitting and detecting an acoustic wave has a key role. A thickness mode piezoelectric transducer is usually used, whose operation frequency is dependent on the thickness of the piezoelectric substrate. Such a conventional type of transducer has a difficulty in high-frequency operation. A surface acoustic wave (SAW) propagates in the form of a leaky wave, when the piezoelectric substrate, sufficiently thicker compared with the wavelength, is in contact with a liquid. In this time, the leaky wave is mode-converted to a longitudinal wave into the liquid. This means that an interdigital transducer (IDT) on the piezoelectric substrate operates at a liquid-solid boundary as a leaky wave transducer for bulk wave radiation into the liquid. The leaky SAW traveling on a sufficiently thick substrate compared with the wavelength has only one mode without velocity dispersion. Thus, conventional transducers such as the thickness mode piezoelectric transducer and the IDT for the leaky SAW have the problem of the limited ultrasound-radiation angle.
An object of the present invention is to provide a device for ultrasound radiation into a material capable of a multi-modes operation and a high efficiency at a high frequency.
Another object of the present invention is to provide a device for ultrasound radiation into a material capable of adjusting ultrasound power.
Another object of the present invention is to provide a device for ultrasound radiation into a material capable of adjusting radiation angle xcex8.
Another object of the present invention is to provide a device for ultrasound radiation into a material capable of sweeping ultrasound beam.
Another object of the present invention is to provide a device for ultrasound radiation into a material capable of a low electric power consumption.
Another object of the present invention is to provide a device for ultrasound radiation into a material capable of radiating an ultrasound into a cellular tissue.
Another object of the present invention is to provide a device for ultrasound radiation into a material excellent in durability and manufacturing.
Another object of the present invention is to provide a device for ultrasound radiation into a material which is not affected by a change in circumstances, for example, a change in temperature.
A still other object of the present invention is to provide a device for ultrasound radiation into a material easy in use and having a small size which is very light in weight and has a simple structure.
According to one aspect of the present invention there is provided a device for ultrasound radiation into a material comprising a piezoelectric substrate, a first input interdigital transducer, a second input interdigital transducer, an output interdigital transducer, an amplifier, and a voltage controller. All the interdigital transducers are formed on one end surface of the piezoelectric substrate.
If an input electric signal is applied to the first input interdigital transducer, a first elastic wave, composed of a leaky- and a non-leaky components, is excited in the piezoelectric substrate. A non-leaky component of the first elastic wave is transmitted to the output interdigital transducer, and detected at the output interdigital transducer as a delayed electric signal, which is amplified via the amplifier. A signal part of an amplified electric signal is fed back, as the input electric signal, to the first input interdigital transducer, again. A remaining signal part of the amplified electric signal is transmitted to the voltage controller, where a voltage of the remaining signal part is controlled, and then, the remaining signal part is applied to the second input interdigital transducer. In this time, a second elastic wave, composed of a leaky- and a non-leaky components, is excited in the piezoelectric substrate. The leaky component of the second elastic wave is radiated effectively in the form of a longitudinal wave, by an intensity corresponding to the voltage of the remaining signal part, into a material kept in contact with the other end surface of the piezoelectric substrate. Thus, it is possible to adjust an ultrasound power into the material.
According to another aspect of the present invention there is provided a piezoelectric substrate made of a piezoelectric ceramic thin plate, the polarization axis thereof being parallel to the thickness direction thereof. Thus, the elastic wave is effectively excited in the piezoelectric substrate.
According to another aspect of the present invention there is provided a piezoelectric substrate made of a piezoelectric polymer thin plate. Thus, the elastic wave is effectively excited in the piezoelectric substrate.
According to another aspect of the present invention there is provided a filter for adjusting a frequency of the input electric signal. A radiation angle xcex8 into the material depends on an operation frequency. Therefore, it is possible to adjust the radiation angle xcex8 into the material.
According to another aspect of the present invention there is provided a polymer film, with which at least a surface part of the other end surface of the piezoelectric substrate is coated. The surface part corresponds to a surface part, including the second input interdigital transducer, of the one end surface of the piezoelectric substrate. Owing to the existence of the polymer film, the longitudinal wave is effectively radiated into the material in contact with an outside surface of the polymer film.
According to other aspect of the present invention there is provided a cap mounted on a surface part, in contact with air, of the other end surface of the piezoelectric substrate. The surface part corresponds to a surface part, including the first input- and the output interdigital transducers, of the one end surface of the piezoelectric substrate. Owing to the existence of the cap, the non-leaky component of the first elastic wave is effectively excited in the piezoelectric substrate, and then transmitted to the output interdigital transducer. Thus, the use of the cap causes a more effective self-oscillation.
According to a further aspect of the present invention there are provided a switch and an input interdigital-transducer group, which is in place of the second input interdigital transducer. The input interdigital-transducer group consists of at least two interdigital transducers, which are connected with the voltage controller in turn via the switch. When the remaining signal part of the amplified electric signal is applied to these interdigital transducers in turn, the leaky component of the second elastic wave is excited, in turn, in zone parts, in the vicinities of these interdigital transducers, respectively, of the piezoelectric substrate. Thus, the leaky component of the second elastic wave is effectively radiated, in turn, in the form of a longitudinal wave into the material. Thus, it is possible to sweep an ultrasound beam into the material.